1. Field of the Invention
This invention relates to engine-operated generator systems, and more particularly to an engine-operated generator system in which the generator is driven as an engine starter.
2. Description of Related Art
FIG. 8 shows a main circuit and a starting control power source circuit in a conventional engine-operated generator system. The conventional engine-operated generator includes a three-phase AC generator AG driven by an engine EG; a rectifier circuit 1 having an inverter transformation function; an inverter transformation circuit 2; a smoothing electrolytic capacitor CD; a starting control power source circuit 4; and a control circuit 5 for controlling main circuit and the starting control power source circuit 4; a DC positive bus P of the main circuit; and a DC negative bus N of the main circuit.
Rectifier circuit 1 includes bridge-connected transistors QR1-QR6 each having a reverse conducting diode D1 and base electrodes b1 connected to receive control pulses S1 from circuit 5. When AC generator AG is driven by the engine EG for power generation, the six diodes D1, which together form a three-phase full-wave rectifier circuit, rectify the three-phase outputs of the AC generator AG into DC outputs.
The inverter transformation circuit 2 is made up of bridge-connected transistors QI1-QI4 each having a flywheel diode D2 and base electrodes b2 connected to receive control pulses S2 from circuit 5, thereby forming a pulse width modulation (PWM) system. The inverter transformation circuit 2 receives the control pulses S2 from control circuit 5 and converts the DC output into a single-phase AC signal when the AC generator AG is in operation. The single-phase AC power is outputted to AC terminals T01 and T02, where it is smoothed by an LC circuit made up of reactor Lo and capacitor Co.
The output thus smoothed is applied to a load (not shown) through output terminals T01 and T02 of the engine-operated generator system. When the AC generator AG is in operation, the six diodes D1, electrolytic capacitor CD, and inverter transformation circuit 2 form a voltage-control inverter.
The starting control power source circuit 4 includes a step up chopper circuit made up of a transistor QC, a reactor LCH, a diode DCH, and a battery BATT. In starting the generator system, the step up chopper circuit is driven by control circuit 5 to apply a predetermined DC voltage to the electrolytic capacitor CD. In this operation, the bridge circuit formed by transistor QR1-QR6 of the rectifier circuit 1 receives control pulses S1 from control circuit 5 and performs an inverter operation to convert the DC voltages into three-phase AC voltages, which are supplied to the AC generator AG. As a result, the AC generator AG carries out power generation to start engine EG. The step up chopper circuit performs this chopping operation until the speed of the engine EG reaches a predetermined value. When the speed of the engine EG reaches the predetermined value, the starting control power source circuit 4 stops its operation, while the inverter transformation circuit 2 starts the inverter transformation operation. Namely, in starting the generator system, the starting control power source circuit 4, the electrolytic capacitor CD, and the bridge circuit of the transistors QR1-QR6 form a voltage control inverter.
The structure of the conventional system is described in more detail.
When the transistor QC of the step up chopper circuit is rendered non-conductive (off) by control circuit 5, the step up chopper circuit is connected to the electrolytic capacitor CD and the battery BATT as shown in FIG. 9. Therefore, no current flows in the step up chopper circuit. When the transistor QC is rendered conductive (on) by a control pulse S3 provided by control circuit 5, the voltage E of the battery is applied across the reactor LCH, so that a current flows as shown in FIG. 10. When the transistor QC is rendered non-conductive (off) while the current is flowing, the current flows to start the electrolytic capacitor CD as shown in FIG. 11. The operation described with reference to FIG. 10 and 11 is repeatedly carried out in order to supply the energy of the battery BATT to the electrolytic capacitor CD.
The conventional system as described in connection with FIGS. 8-11 has the following disadvantages: as is apparent from the above description, the starting control power source circuit 4 is essential in order to start engine EG in the conventional engine-operated generator system. Accordingly, the number of components is high, and the system tends to have a rather intricate circuit arrangement and is unavoidably bulky. Furthermore, the DC positive bus of the main circuit is different in potential than the positive terminal of the battery BATT, and the DC negative bus is different in potential than the negative terminal of the battery, making it difficult to obtain a control voltage from the battery BATT with a common potential.